Armed Islamist opposition fighters have used yellow phosphorous in a chemical attack on the Sheikh Maqsood neighborhood in the Syrian city of Aleppo on Tuesday, Kurdish militia group YPG said.

“We hereby inform you that on March 8, 2016 at 15:00, shelling [was carried out] with rockets that carry chemical material, which we believe to be yellow phosphorous chemical weapon, on Sheikh Maqsud neighborhood by the Syrian armed opposition factions and battalions,” Redur Xelilm, YPG’s spokesman, said in a statement.

“We saw something flying and then there was an explosion, the building collapsed just in a few seconds,” a witness told RT’s Phelan. Overall, nine buildings have been reduced to rubble.

Aleppo’s Sheikh Maqsood neighborhood, which is controlled by Kurdish militia, is of strategic importance to all the warring sides.

The internationally-backed deal aimed at securing a “cessation of hostilities” in Syria between government forces and armed opposition groups was implemented on February 27 and is being monitored by a co-chaired task force. It was reported that 97 armed groups operating in Syria have agreed to its conditions, though Islamic State (IS, ISIS/ISIL), Al Nusra Front, and other terrorist organizations are excluded.

There have been numerous reports of violations since the ceasefire regime came into effect, however, most being observed in the Aleppo province.

Reports and videos from the ground suggest that Turkey is one of the sides disrupting the tentative Syrian ceasefire. According to YPG forces, Turkish artillery has been shelling its positions in Aleppo, hampering Kurdish militia operations against Al-Nusra Front.

“We’re constantly raising these issues. They are already being discussed in Geneva, and in individual cooperation formats under the aegis of the UN,” Russian Deputy Foreign Minister Mikhail Bogdanov said on Monday, referring to Turkey’s repeated breaches of the truce in the Syrian provinces of Aleppo and Idlib.